For many years greenhouses have been used to provide a suitable growing environment for various plants in areas where the climate is not optimum or conducive to their growth. Where the natural sunlight is not of sufficient intensity and/or duration needed to promote optimum growth of the desired vegetation, artificial lighting has been incorporated in growth chambers and greenhouses to provide or supplement natural sunlight. Various types of lighting have been developed over the years in an attempt to more accurately replicate natural sunlight. Until recently, the most effective types of lighting used in greenhouses, included, florescent, metal halide and high-pressure sodium vapor. Each type has its advantages and disadvantages but all provide much of the light spectrum, provided by the sun, needed to produce photosynthesis. Unfortunately, they also provide wavelengths of light that are not efficient or at all useful in supporting photosynthesis, and thus, waste energy. Recently, Light Emitting Diode (LED) lights have entered the picture, offering a more targeted spectrum of light wavelengths, while at the same time increasing lighting efficiency.
Research shows that the most efficient production of photosynthesis occurs when plants are exposed to primarily the blue and red wavelength regions of the light spectrum, referred to in the industry as Photosynthetically Active Radiation (PAR), spanning the visible spectrum from roughly 400 to 700 nm. As indicated above, legacy lighting types (florescent, metal halide, and high-pressure sodium vapor), produce full spectrum lighting and in doing so waste power in the green, yellow and orange wavelengths offering limited, if any, benefit photosynthetically. Currently available LED lighting fixtures are capable of providing some wavelengths of light required to support photosynthetic activity (PA), but are grossly limited in the number of different wavelengths, typically two, provided, and the intensity of these cannot be independently adjusted.
Further research has shown that various plants require slightly different wavelengths than others to induce optimum photosynthetic activity. In addition, a given type of plant may require more of the blue wavelength light at one point in its growth, while benefiting from a higher concentration of red wavelength light at another point (e.g., vegetative growth versus fruit developing/ripening). LED lighting has been found to be superior to other types of grow lights in providing PAR light.
Research also suggests that plants may respond positively to a slowly increasing and decreasing light source of varying wavelengths when turning on and off, mimicking that of natural sunlight over the duration of a day. Another point regarding plant growth lighting needs is that there is an upper limit to the intensity of light required to produce optimum photosynthetic activity.